Preprints
https://doi.org/10.5194/os-2021-64
https://doi.org/10.5194/os-2021-64

  08 Jul 2021

08 Jul 2021

Review status: this preprint is currently under review for the journal OS.

Assimilating realistically simulated wide-swath altimeter observations in a high-resolution shelf-seas forecasting system

Robert R. King and Matthew J. Martin Robert R. King and Matthew J. Martin
  • Met Office, Exeter, UK

Abstract. The impact of assimilating simulated wide-swath altimetry observations from the upcoming SWOT mission is assessed using Observing System Simulation Experiments (OSSEs). These experiments use the Met Office 1.5 km resolution North-West European Shelf analysis and forecasting system. In an effort to understand the importance of future work to account for correlated errors in the data assimilation scheme, we simulate SWOT observations with and without realistic correlated errors. These are assimilated in OSSEs along with simulated observations of the standard observing network, also with realistic errors added.

It was found that while the assimilation of SWOT observations without correlated errors reduced the RMSE in sea surface height (SSH) and surface current speeds by up to 20 %, the inclusion of correlated errors in the observations degraded both the SSH and surface currents, introduced an erroneous increase in the mean surface currents, and degraded the sub-surface temperature and salinity. While restricting the SWOT data to the inner half of the swath and applying observation averaging with a 5 km radius negated most of the negative impacts, it also severely limited the positive impacts. To realise the full benefits in the prediction of the ocean mesoscale offered by wide-swath altimetry missions it is crucial that methods to ameliorate the effects of correlated errors in the processing of the SWOT observations and to account for the correlated errors in the assimilation are implemented.

Robert R. King and Matthew J. Martin

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-64', Anonymous Referee #1, 26 Jul 2021
  • RC2: 'Comment on os-2021-64', Anonymous Referee #1, 26 Jul 2021
  • RC3: 'Comment on os-2021-64', Anonymous Referee #2, 10 Sep 2021

Robert R. King and Matthew J. Martin

Robert R. King and Matthew J. Martin

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Short summary
The SWOT satellite will provide a step change in our ability to measure the sea surface height over large areas, and so improve operational ocean forecasts, but will be affected by large correlated errors. We found that while SWOT observations without these errors significantly improved our system, including correlated errors degraded most variables. To realise the full benefits offered by the SWOT mission, we must develop methods to account for the correlated errors in our systems.